STEM-OPT Online application

what are the Approve ration for STEM-OPT? What thing they main check while applying online ?

If you are talking about the first time post competition OPT, your DSO will issue a new I-20 recommending OPT and you simply fill out the I-765 and submit it along with I-20 and other supporting documents.
Work closely with your DSO and they will guide you through the process.